well know let’s fix it in FireF0x:
1, While in Firefox click the Orange Firefox button and add-ons.

2, Now the add-on window will be opened. Now Look for the search bar on Top Right and Search “User agent Switcher” and when search completes and the results come click on the install button and Restart Firefox.
3 If you don’t see the plugin’s icon in the navigation bar, right-click the navigation bar and select Customize.